The invention set forth in this specification pertains to a feed system for introducing metallic scrap into a rotary kiln or other type of heating oven. The invention is primarily intended to be used and is considered to have its primary utility in connection with conveying aluminum scrap into a rotary kiln used to clean the scrap prior to reclaiming the aluminum.
Since rotary kilns used to clean or dry aluminum scrap are generally of a large radius and are also inclined such that the inlet end is of higher elevation than the outlet end, it is necessary to raise the scrap in order to introduce it into the kiln. Additionally it is desirable to isolate the kiln from the ambient atmosphere to prevent escape of vapors from the kiln to the ambient atmosphere and to inhibit the introduction of cool ambient air into the kiln. Generally material is raised to the inlet opening of the kiln with a conveyor. A wide variety of different conveyors can be utilized for this purpose and among such conveyors are "endless conveyors" constructed so as to have a surface for supporting the material and lift flights extending outwardly from this surface at periodic intervals along the length of the surface. Conveyors of this type can be endless belt conveyors utilizing a continuous or endless belt to provide such a surface and having lifters or flights attached to the belt so as to extend from it.
More commonly such conveyors are what are referred to as "apron" conveyors. Such conveyors are generally constructed so as to utilize an endless chain type mechanism to support and carry overlapping or closely adjacent plates or pans used to provide a supporting surface as indicated in the preceding. It is common to attach lifts or flights to such aprons or pans. It will be realized that both of these types of conveyors can be utilized as conveyors without such lifters or flights. However, the use of such lifters or flights is considered to be necessary in order to prevent material from sliding back on such conveyors when such conveyors are oriented so as to extend at an angle to the horizontal.
The amount which such a conveyor is inclined so as to extend at an angle to the horizontal is normally limited so as to avoid a conveyor going upwardly at an angle sufficiently great so that the material will slide back along the length of the conveyor. Thus, for example, the Chemical Engineer's Handbook by Perry, Third Edition, McGraw-Hill Book Company, Inc., 1950, contains the following statement relative to flight conveyors (page 1347):
"The conveyor may be inclined up to a point where the load begins to flow backward over the tops of the flights. The limit is about thirty degrees. The capacity becomes smaller as the slope increases."
Although this statement is in respect to the use of flights as essentially pushers to push along a material as such material is conveyed, it is considered applicable to conveyors as noted in the preceding having a supporting surface and having flights extending outwardly from this surface.
In the use of known conveyors for the purpose of elevating metal scrap such as aluminum scrap certain problems have been noted which are considered to be reasonably unique to the movement of such scrap. In general, such scrap tends to consist of metal particles such as lathe turnings, chunks of sheet metal of various sizes and shapes and the like, of an extremely non-uniform character contaminated with various different organic and inorganic materials. These contaminants can effect the manner in which such particles tend to adhere to one another and/or separate from one another.
Because noxious and irritating vapors are produced in drying and cleaning kilns it is necessary when said vapors are present to seal such a kiln from the immediate environment. Additionally since these kiln or heating ovens generally utilize hot gases to dry and clean the scrap metal, the introduction of cool ambient air into the kiln or heating oven during introduction of scrap into the oven lowers the temperature of the gases in the oven and therefore effects the operation of the kiln or heating oven. Typically a conventional screw-type feed system has been used to charge kilns; however, since the aluminum scrap metal particles are of a non-uniform character as described above, they cannot be conveniently fed into rotary kilns through a conventional screw-type feed system which requires rather uniformly and relatively small sized particles in order to work efficiently.
The present invention is based upon a recognition that conventional "endless" conveyors have not been particularly effective in moving scrap from a pile of scrap and/or a hopper at a controllable rate and further, since said scrap is of a non-uniform size conventional screw-type feed systems are also disadvantageous. Further the present invention is based upon a recognition that such conventional conveyors tend to take up an inordinate amount of floor space when operated in a conventional manner because of the relatively small angle to the horizontal at which they can be located, and when this is coupled with a screw-type feed system projecting horizontally from the kiln inlet an additional amount of floor space is required.